Composite materials have become valuable construction materials in aerospace, defense and in recent years in automotive industry. The advantage of composite materials over conventional materials stems largely from their higher specific strength, stiffness and fatigue characteristics. Composite components are joined by mechanical fasteners, accurate, precise high quality holes need to be drilled to ensure proper and durable assemblies. Drilling of composite materials causes several damages, such us: delamination, fibre-pull out, edge chipping, uncut fibers and others. Delamination is a major problem associated with drilling fiber reinforced composite materials. It causes poor assembly tolerance, reduces structural integrity of material and the potential for long term performance deterioration. The thrust force has been cited as main cause of delamination. In this paper the objective was to establish correlation between cutting parameters and thrust force, drilling torque and delamination. Drilling tests were carried out on carbon epoxy composite material using three different drills, HSS-Co twist drill, Multi Constructional twist drill and "Brad & Spur" drill. The data have been processed by the "DesignExpert" software package which generated the mathematical models.